The present invention relates to image scanning apparatus and in particular to such apparatus comprising a profiling surface; a feed mechanism for feeding a flexible radiation sensitive record medium across the profiling surface; and a scanning system for scanning a modulated radiation beam across the record medium to expose the record medium.
A conventional internal drum imagesetter is illustrated in the schematic end view of FIG. 5. A drum 50 has a semi-cylindrical internal profiling surface 51. A film 52 is mounted on the surface by attaching one end of the film to a loading carriage 53 which traverses round the drum. After the film has been loaded, it is exposed by a scanning radiation beam 54.
The imagesetter of FIG. 5 suffers from the problem that the film 52 will not conform precisely with the profile of the surface 51. Therefore the loading carriage will load more than the required length of film into the imagesetter.
In accordance with a first aspect of the present invention there is provided image scanning apparatus comprising a profiling surface; a feed mechanism for feeding a flexible radiation sensitive record medium across the profiling surface; a scanning system for scanning a modulated radiation beam across the record medium to expose the record medium; and a pressurizer operable simultaneously with the feed mechanism to generate a pressure difference between opposed sides of the record medium as it is fed across the profiling surface whereby the record medium engages the profiling surface and conforms with the shape of the profiling surface.
In accordance with a second aspect of the present invention there is provided a method of loading a flexible radiation sensitive record medium into an image scanning apparatus, the method comprising feeding a flexible radiation sensitive record medium across a profiling surface; generating a pressure difference between opposed sides of the record medium as it is fed across the profiling surface whereby the record medium engages the profiling surface and conforms with the shape of the profiling surface; and scanning a modulated radiation beam across the record medium to expose the record medium.
By applying a pressure difference to the record medium during the loading operation we ensure that the record medium conforms to the profiling surface during loading, and as a result the correct length of record medium is loaded into the apparatus.
The conventional imagesetter of FIG. 5 also suffers from the problem of dust particlesxe2x80x94ie. dust particles can fall directly onto the film 52 and will either adhere to the film or fall down to the lower region 55 of the imagesetter. Dust particles can also collect on the surface 51 when a film is not present. The loading arrangement of the present invention enables the profiling surface to be oriented in alternative ways to reduce the problems causes by dust particles. For example the profiling surface can be oriented such that the normal to the profiling surface does not point directly upwards at any point. In addition it will be noted that the conventional imagesetter of FIG. 5 is oriented such that the normal to the surface 51 points upwards in the range of angles 0xc2x0-90xc2x0, and 270xc2x0-360xc2x0 (with gravity g pointing directly downwards at 180xc2x0). As a result the surface 51 provides a reaction force to the gravitational force of the film 52 at all points (except at the extreme edges). In contrast, the normal to the profiling surface in the present invention can point in any direction, including downwards, ie. in the range of angles 90xc2x0-270xc2x0 (in which the surface provides no reaction force and the record medium is supported by the pressure difference).
In other words, compared to the orientation of FIG. 5, the profiling surface can be oriented on its side (or even upside down) to prevent dust from falling or collecting on the profiling surface or the record medium. Similarly, a flat-bed scanner with a planar surface can be oriented with its planar profiling surface at an angle, or even upside down.
The pressurizer may generate a vacuum on one side of the record medium. However preferably the pressurizer increases the pressure on one side of the record medium.
Typically the pressurizer comprises a pressure chamber defined by a plurality of walls including the profiling surface, and means for increasing the pressure in the pressure chamber. The use of a pressure chamber ensures a relatively uniform pressure and also reduces the power requirements.
Typically the pressure chamber has one or more openings (e.g., slots) adjacent the profiling surface. This enables gas to exit from the pressure chamber in a controlled manner. By positioning the opening(s) adjacent the profiling surface we ensure that any gas flow acts to force the record medium against the profiling surface.
The profiling surface may be planar but in a preferred embodiment the profiling surface is curved, eg semi-cylindrical.